ABSTRACT This work presents a time-transit study of the interaction of short laser pulses with ag... more ABSTRACT This work presents a time-transit study of the interaction of short laser pulses with agar-gel tissue phantoms. By using a pump-probe laser system, the phenomenon of laser-induced bubble formation in the agar gel is optically imaged onto a CCD; the design of the experimental set up allows us to record both the launching and the propagation of the shockwave that is the precursor to the bubble expansion. Laser-induced bubble formation and acoustic/shock wave propagation have been extensively investigated in water, whereas very few studies incorporate biological tissues or even tissue models such as agar gels.
Applied Physics a Materials Science Processing, Jan 5, 2011
A 1D photonic crystal structure contains 16 layers, 8 common dielectric layers and 8 layers with ... more A 1D photonic crystal structure contains 16 layers, 8 common dielectric layers and 8 layers with nonlinear medium, with an arrangement similar to the 5th generation, Thue-Morse multilayer is presented. The properties of photonics band gap, field distribution and optical multistability are investigated. On the band gap, 5 resonant modes is observed. On the behavior of output intensity versus input intensity around resonant frequencies, the multistability response observed. When the frequency of incident field is close to the resonant frequency, the threshold intensity of multistability is decreased.
In this paper we developed the Thermal transfer mechanism in the Carbon Nano-Tubes (CNTs) 15nm ch... more In this paper we developed the Thermal transfer mechanism in the Carbon Nano-Tubes (CNTs) 15nm channel length, we analyzed transfer phenomena by new methods of Modern Quantum Mechanics to distribute Dirac thermal equation in two dimensions when the structure's dimension is in the order of Broglie wave length, and it has shown completely that depending on the dynamics of the heat that carriers scattering the damped or oscillated temperature field can be generated in CNTs. When the laser pulse generates relativistic electrons the cross section for the generation of electron-positron pairs is equal to the Thomson cross section.
"A 1D photonic crystal structure contains 16 layers, 8 common dielectric layers ... more "A 1D photonic crystal structure contains 16 layers, 8 common dielectric layers and 8 layers with nonlinear medium, with an arrangement similar to the 5th generation, Thue–Morse multilayer is presented. The properties of photonics band gap, field distribution and optical multistability are investigated. On the band gap, 5 resonant modes is observed. On the behavior of output intensity versus input intensity around resonant frequencies, the multistability response observed. When the frequency of incident field is close to the resonant frequency, the threshold intensity of multistability is decreased. "
The luminescence parameters of laser-induced bubble in the presence of an acoustic field in water... more The luminescence parameters of laser-induced bubble in the presence of an acoustic field in water are studied. A comparison is made between parameters such as bubble radius, interior temperature, and pressure of the bubble induced by laser and an acoustic field influenced by different driving pressure amplitudes. It is found that the bubble volume induced by laser at the collapse instant is more than 10(6) times larger than the one induced by an acoustic field. It is also noticed, by increasing the driving pressure amplitude, the bubble radius decreases in both cases, however, the bubble interior pressure and temperature increase.
A class of electro-optically tunable metamaterial absorbers is designed and theoretically investi... more A class of electro-optically tunable metamaterial absorbers is designed and theoretically investigated in the infrared regime towards realizing free-space amplitude modulators. The spacer between a subwavelength metallic stripe grating and a back metal reflector is occupied by a bilayer of indium tin oxide (ITO) and hafnium oxide (HfO 2). The application of a bias voltage across the bilayer induces free-carrier accumulation at the HfO 2 /ITO interface that locally modulates the ITO permittivity and drastically modifies the optical response of the absorber owing to the induced epsilon-near-zero (ENZ) effect. The carrier distribution and dynamics are solved via the drift–diffusion model, which is coupled with optical wave propagation studies in a common finite-element method platform. Optimized structures are derived that enable the amplitude modulation of the reflected wave with moderate insertion losses, theoretically infinite extinction ratio, sub-picosecond switching times and low operating voltages.
In this paper, the femtosecond laser-induced darkening in SK3 glass is investigated. A sample wit... more In this paper, the femtosecond laser-induced darkening in SK3 glass is investigated. A sample with 3-mm thickness is irradiated with 200 fs laser pulses (FLP) at 800 nm wavelength and 1 kHz repetition rate. When a piece of quartz or sapphire, which does not show darkening effect under IR irradiations, is placed in front of the sample, the laser-induced darkening is enhanced. The directly darkened region in the sample gets darker on placing a piece of quartz or sapphire in front of the sample. When a piece of ULE glass that shows darkening effect by IR-FLP irradiations is placed in front of the sample, SK3 sample does not get that dark. We believe the enhancement of the darkening in SK3 glass sample by the quartz or sapphire is related to the absorption of the short wavelength component of the white light, which is generated and not absorbed in the quartz or sapphire.
Conversion efficiency of second-harmonic generation (SHG) in a multicrystal structure arrangement... more Conversion efficiency of second-harmonic generation (SHG) in a multicrystal structure arrangement , under linearly absorption of interacting waves was analytically investigated. Different linear absorption and nonlinear interaction coefficients were considered for both of the fundamental and the second harmonic waves in cascade layers. The intensity-constant approximation on fundamental wave radiation was applied in calculations. Behavior of conversion efficiency with interaction coherence length of fundamental wave, phase miss-matching and ratio of linear absorption coefficients were graphically illustrated. The results are shown that in multicrystal structure scheme, the conversion efficiency can be tuned by the interaction coherent length and it is possible to compensate the phase differences induced in the previous layers. The phase compensation between the layers is the physical reason of efficiency improvement.
ABSTRACT This work presents a time-transit study of the interaction of short laser pulses with ag... more ABSTRACT This work presents a time-transit study of the interaction of short laser pulses with agar-gel tissue phantoms. By using a pump-probe laser system, the phenomenon of laser-induced bubble formation in the agar gel is optically imaged onto a CCD; the design of the experimental set up allows us to record both the launching and the propagation of the shockwave that is the precursor to the bubble expansion. Laser-induced bubble formation and acoustic/shock wave propagation have been extensively investigated in water, whereas very few studies incorporate biological tissues or even tissue models such as agar gels.
Applied Physics a Materials Science Processing, Jan 5, 2011
A 1D photonic crystal structure contains 16 layers, 8 common dielectric layers and 8 layers with ... more A 1D photonic crystal structure contains 16 layers, 8 common dielectric layers and 8 layers with nonlinear medium, with an arrangement similar to the 5th generation, Thue-Morse multilayer is presented. The properties of photonics band gap, field distribution and optical multistability are investigated. On the band gap, 5 resonant modes is observed. On the behavior of output intensity versus input intensity around resonant frequencies, the multistability response observed. When the frequency of incident field is close to the resonant frequency, the threshold intensity of multistability is decreased.
In this paper we developed the Thermal transfer mechanism in the Carbon Nano-Tubes (CNTs) 15nm ch... more In this paper we developed the Thermal transfer mechanism in the Carbon Nano-Tubes (CNTs) 15nm channel length, we analyzed transfer phenomena by new methods of Modern Quantum Mechanics to distribute Dirac thermal equation in two dimensions when the structure's dimension is in the order of Broglie wave length, and it has shown completely that depending on the dynamics of the heat that carriers scattering the damped or oscillated temperature field can be generated in CNTs. When the laser pulse generates relativistic electrons the cross section for the generation of electron-positron pairs is equal to the Thomson cross section.
"A 1D photonic crystal structure contains 16 layers, 8 common dielectric layers ... more "A 1D photonic crystal structure contains 16 layers, 8 common dielectric layers and 8 layers with nonlinear medium, with an arrangement similar to the 5th generation, Thue–Morse multilayer is presented. The properties of photonics band gap, field distribution and optical multistability are investigated. On the band gap, 5 resonant modes is observed. On the behavior of output intensity versus input intensity around resonant frequencies, the multistability response observed. When the frequency of incident field is close to the resonant frequency, the threshold intensity of multistability is decreased. "
The luminescence parameters of laser-induced bubble in the presence of an acoustic field in water... more The luminescence parameters of laser-induced bubble in the presence of an acoustic field in water are studied. A comparison is made between parameters such as bubble radius, interior temperature, and pressure of the bubble induced by laser and an acoustic field influenced by different driving pressure amplitudes. It is found that the bubble volume induced by laser at the collapse instant is more than 10(6) times larger than the one induced by an acoustic field. It is also noticed, by increasing the driving pressure amplitude, the bubble radius decreases in both cases, however, the bubble interior pressure and temperature increase.
A class of electro-optically tunable metamaterial absorbers is designed and theoretically investi... more A class of electro-optically tunable metamaterial absorbers is designed and theoretically investigated in the infrared regime towards realizing free-space amplitude modulators. The spacer between a subwavelength metallic stripe grating and a back metal reflector is occupied by a bilayer of indium tin oxide (ITO) and hafnium oxide (HfO 2). The application of a bias voltage across the bilayer induces free-carrier accumulation at the HfO 2 /ITO interface that locally modulates the ITO permittivity and drastically modifies the optical response of the absorber owing to the induced epsilon-near-zero (ENZ) effect. The carrier distribution and dynamics are solved via the drift–diffusion model, which is coupled with optical wave propagation studies in a common finite-element method platform. Optimized structures are derived that enable the amplitude modulation of the reflected wave with moderate insertion losses, theoretically infinite extinction ratio, sub-picosecond switching times and low operating voltages.
In this paper, the femtosecond laser-induced darkening in SK3 glass is investigated. A sample wit... more In this paper, the femtosecond laser-induced darkening in SK3 glass is investigated. A sample with 3-mm thickness is irradiated with 200 fs laser pulses (FLP) at 800 nm wavelength and 1 kHz repetition rate. When a piece of quartz or sapphire, which does not show darkening effect under IR irradiations, is placed in front of the sample, the laser-induced darkening is enhanced. The directly darkened region in the sample gets darker on placing a piece of quartz or sapphire in front of the sample. When a piece of ULE glass that shows darkening effect by IR-FLP irradiations is placed in front of the sample, SK3 sample does not get that dark. We believe the enhancement of the darkening in SK3 glass sample by the quartz or sapphire is related to the absorption of the short wavelength component of the white light, which is generated and not absorbed in the quartz or sapphire.
Conversion efficiency of second-harmonic generation (SHG) in a multicrystal structure arrangement... more Conversion efficiency of second-harmonic generation (SHG) in a multicrystal structure arrangement , under linearly absorption of interacting waves was analytically investigated. Different linear absorption and nonlinear interaction coefficients were considered for both of the fundamental and the second harmonic waves in cascade layers. The intensity-constant approximation on fundamental wave radiation was applied in calculations. Behavior of conversion efficiency with interaction coherence length of fundamental wave, phase miss-matching and ratio of linear absorption coefficients were graphically illustrated. The results are shown that in multicrystal structure scheme, the conversion efficiency can be tuned by the interaction coherent length and it is possible to compensate the phase differences induced in the previous layers. The phase compensation between the layers is the physical reason of efficiency improvement.
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